Glutamate, the major excitatory transmitter in the central nervous system, is crucial not only for synaptic transmission but also for long-term neuronal changes such as synaptic plasticity and control of gene expression. Many of the actions of glutamate are exerted through a specific receptor, the N-methyl-D- aspartate receptor (NMDAR), which controls the trafficking of a second glutamate receptor, the a-amino-3- hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR). Recently, in collaboration with Dr. Josep Dalmau, we identified two distinct encephalitic syndromes, associated directly with antibodies to NMDAR in one syndrome and with antibodies to the AMPAR in the other. In antiAMPAR encephalitis, subjects present with symptomatology (amnesia, seizures) analogous to that predicted to occur with AMPAR hypofunction. However, the syndrome can be treated in some individuals by tumor removal or plasmapheresis, suggesting that it is mediated directly by antibodies. Patients with this syndrome make antibodies to the extracellular portion of the AMPAR subunits GluR1 and/or GluR2. Our new preliminary data have identified structural determinants in the amino terminal domain (ATD) of GluR1/2 that are necessary for immunoreactivity to patients' antiAMPAR antibodies. We have also used fusion proteins from these regions to demonstrate diversity in the immune response and to identify individuals with possible antiAMPAR encephalitis who tested negatively by previous approaches. In this proposal we will continue to create new tools for investigation of patients' antiAMPAR antibodies in order to assess whether this syndrome is dramatically under diagnosed, and to link the pathophysiology to specific AMPAR portions First, we will test for the presence of antiAMPAR antibodies and antibodies to specific structural determinants on the AMPAR in samples from a large cohort of individuals with potential encephalitis. We will then correlate the results with clinical features of the subjects and determine whether pathophysiological mechanisms in anti AMPAR encephalitis are mediated through specific epitopes. Cumulatively, completion of these aims will lead to improved understanding of the pathophysiological mechanisms in this disorder, develop tools for further exploration of the mechanisms, and potentially allow creation of novel therapeutic approaches for antiAMPAR encephalitis.